This section introduces aspects that may be helpful in facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
In some known asynchronous virtual machine (VM) replication systems, primary-backup methods must synchronize the primary's state with a backup before the messages from the primary may be sent to the environment. In these embodiments, the primary buffers output messages, sends state information to the backup, waits for acknowledgement from the backup and then releases the buffered messages to the environment. The primary buffers messages because if messages are released immediately to the environment, the environment and the backup will have differing views of the primary state. This inconsistency may result in an application error. Thus, these backup methods may introduce delay in the communication from the primary to the environment arising from the primary-backup synchronization. In some known systems, primary-backup communications are provisioned for low latency in order to obtain adequate network performance. Low latency provisioning may require an expensive, high-speed interconnection, or a compromise on fault-tolerance by placing the primary and backup physically close together.